reCAPTCHA™ works by supplying 2 words (or occasionally names or numbers) scanned from books in an effort to fully digitize them. One of these words is known, the other is not. Your answer for the known word is checked, allowing you to send the email. The answer you provide for the unknown word is then added to their database to be verified by other users of the reCAPTCHA™ applet on sites around the world. For more info on how reCAPTCHA™ works, visit their site.